Stressed-skin span structure



May 7, 1968 R. BRANDWEIN 3,381,432

S'I'RESSED-SKIN SPAN STRUCTURE Filed Sept. 19, 1966 INVENTOR Rowland Brondwein ATTORNEYS United States Patent 01 3,381,432 STRESSED-SKIN SPAN STRUCTURE Rowland Brandwein, Newton, Conn., assignor to Inventors Group, Newton, Conu., a ctr-partnership composed of Francis H. Bette, Joseph S. Bette, Rowland Brand- Wein, and George A. Tomey Filed Sept. 19, 1966, Ser. No. 580,266 Claims. (Cl. 52-309) This invention relates to a self-supporting structure that is capable of spanning relatively large distances with out the need for extraneous intermediate supports or buttresses, and in particular to a span structure employing a stressed-skin construction that is capable of supporting relatively large loads along the entire length of the unsupported span.

It has heretofore been proposed that channel-shaped beam members formed of sheet metal or the like be employed to span or roof over open areas such as the roof area of a building or the like. In this known roofing construction the channel-shaped sheet metal beam members are arched slightly, and the arched beam members are assembled side by side over the area to be covered. The open channel of each channel-shaped beam member faces upwardly, and the upper edges of the adjacent beam members are secured together by sheet metal interlocking joints, or screws, or the like. The upwardly facing open channel of each beam member is advantageously filled with an insulating material such as rock wool or fiber glass or the like, and then the entire roofing structure is covered over with conventional roofing board and Waterproofing materials.

Although the aforementioned roofing construction possesses many advantages, it is not capable of spanning very great distances (generally less than feet) and and in addition has very limited load bearing capabilities. After an extensive investigation of the problem of erecting self-supporting roofing structures capable of spanning greater distances and of supporting greater loads than the type of roofing structure hereinbefore described, I have now developed a new self-supporting span structure that employs a stressed-skin construction that greatly increases the longitudinal distance that can be spanned by the structure and at the same time greatly increases the load that can be supported along the entire length of the span structure. Specifically, field tests have demonstrated that the stressed-skin span structure of my invention can span distances more than 120 feet between the supporting piers of the structure (e.g., the walls of a building) and further can support a load in excess of 100 pounds per square foot of roof area.

My new self-supporting, stressed-skin span structure comprises at least two layers of channel-shaped beam members extended longitudinally from one span support member to a second span support member that is spaced an appreciable distance therefrom. The channel-shaped beam members in each layer are disposed side by side in contact with each other and in contact with the under surface of the channel-shaped beam members in the layer disposed directly thereover. Each channel-shaped beam member is made up of a longitudinally extending main body portion and upstanding side rail portions that are disposed along each longitudinal edge of the main body portion generally perpendicular thereto. The open channels of the beam members in each layer face upwardly and advantageously are disposed in staggered relationship with respect to the channel-shaped beam members in the layer positioned immediately thereover. The upper longitudinal edges of the upstanding side rail portions of the channel-shaped beam members in the underlying layer of beam members are secured to the underside of the main body portion of the channel-shaped beam bee member disposed immediately thereover approximately advantageously but not necessarily along the longitudinal center line of each of said beam members. It will be seen, therefore, that the longitudinally extending main body portions of the channel-shaped beam members of one layer of said beam members and the longitudinally extending main body portions of the beam members in an adjoining layer of said beam members are firmly connected together by the upstanding side rail portions of the channel-shaped beam members in the underlying layer. As a consequence, the thus interconnected main body portions of the beam members in adjoining layers form a stressed-skin structure that is capable of supporting relatively large loads that are substantially in excess of the aggregate load that could be supported by the individual components of the span structure.

The box-like longitudinal voids formed by each channel-shaped beam member and the under surface of the main body portions of the beam members disposed directly thereover are advantageously substantially completely filled with a lightweight rigid core material that has a relatively low density and that advantageously is adherent tothe inner surfaces of the void. The lightweight core material should be rigid and should have high compressive strength and high beam strength (that is, resistance to bending). The incorporation. of the lightweight core material in the longitudinal voids greatly enhances the strength and rigidity of the stressed-skin structure formed by the longitudinally extending main body portions of the beam members in one layer and the longitudinally extending main body portions of the beam members in the adjoining layers of said beam members.

The stressed-skin span structure of my invention requires a minimum of two layers of interconnected channel-shaped beam members. Such two-layer span structures spanning a distance of about 40 feet have been shown to be capable of supporting loads in excess of pounds per square foot, and such span structures can span a distance in excess of 120 feet. Moreover, the load-bearing capability of the stressed-skin structure can be greatly increased both by incorporating a lightweight core material in the longitudinal voids between the several layers of the structure and by increasing the number of layers of channel-shaped beam members in the structure.

At present, the stressed-skin span structure of my invention is used primarily to span and roof over large areas of open buildings. The span structure can also be used as a structural member for pedestrian or vehicular bridges, or as a support or form for poured concrete bridges. Other uses for my stressed-skin span structure will be apparent from the following description thereof in conjunction with the accompanying drawings, of which:

FIG. 1 is a perspective view of an advantageous embodiment of my stressed-skin span structure,

FIG. 2 is a fragmentary perspective view of one of the channel-shaped beam members employed in my span structure,

FIG. 3 is a sectional view along line 3-3 of FIG. 1 showing the relationship of two layers of channel-shaped beam members assembled in accordance with my invention,

FIG. 4 is a sectional view similar to FIG. 3 of a span structure made up of four layers of channel-shaped beam members assembled in accordance with my invention, and

FIG. 5 shows sectional views of some of the various modifications of the channel-shaped beam member that may be employed in the span structure of my invention.

As shown in FIG. 1, the stressed-skin, self-supporting span structure of my invention comprises a plurality of layers 11a, 11b of channel-shaped beam members 12 which extend longitudinally from one span support member 13 to a second span support member 14 spaced an appreciable distance therefrom. The span support members 13 and 14 are of any conventional construction suitable for the purpose for which the span structure is being employed. For example, if the span structure of my invention is being employed to cover or roof over a large open building, the span support members comprise the side walls of the building which may be of conventional post and beam or cinder block construction. Similarly, if the span structure is being employed as a part of a bridge or other heavy-duty, load-bearing structure, the span support members are advantageously formed of reinforced concrete or masonry. The stressed-skin span structure is advantageously slightly arched as shown in FIG. I particularly if the span structure is to carry an appreciable load. Ordinarily, the minimum ratio of the height of the arch to the length of the span is in the order of about 0.15, this span height to span length ratio being suflicient to provide enough load-bearing capability to meet the stringent building code requirements for exterior roofing structures in Northeastern United States. Of course, for greater loads the ratio of span height to span length of the span structure can be increased as necessary, and for small or negligible loads the span to height to length ratio can be negligible.

As shown best in FIG. 2, the individual channelshaped beam members 12 from which the span structure is constructed each comprises a longitudinally extending main body portion 16 along each longitudinal edge of which are disposed upstanding side rail portions 17 generally perpendicular to the main body portion. Flange portions 18 are advantageously disposed along the upper longitudinal edges of each side rail portion 17 generally perpendicular thereto, the flange portions advantageously being turned inwardly as shown in FIG. 2. However, the flange portions 18 may have other configurations as hereinafter explained. The beam members 12 are advantageously formed of sheet metal, and in a typical case the beam member measures about 2 inches in height, 6 inches in width and up to 120 feet in length.

The channel-shaped beam members 12 are assembled in a plurality of layers 11a, 11b, etc. of beam members as shown in FIGS. 3 and 4. The beam members 12 in each layer 11 are disposed side by side with the side rail portions 17 of adjoining beam members in close proximity, or in actual contact, with each other, and with the main body portions 16 of the beam members in substantially horizontal alignment as clearly shown in FIG. 3. The beam members 12 in adjoining layers 11a and 11b are advantageously disposed in staggered relationship as shown in FIGS. 3 and 4, and the flange portions 1 8 of the beam members 12 in the underlying layer 11a are secured to the under surface of the main body portion 16 of the beam members 12 of the overlying layer 11b usually along the longitudinal center line of the overlying beam members. The flange portions 18 of the underlying beam members 12 are secured to the under surface of the main body portions 16 of the overlying beam members by any suitable means such, for example, as sheet metal screws, blind riveting, welding or the like. However, I presently prefer to secure the flange portions 18 to the main body portions 16 by means of an adhesive material such as an epoxy or polyurethane resin based adhesive. Moreover, the adhesive material is advantageously in the form of a fabric reinforced plastic tape 20 which is applied first to the upper surfaces of adjoining flange portions 18 of the beam members 12 in the lower layer 11a, the beam members 12 in the upper layer 11b then being positioned over the tape 20 of adhesive material as shown in FIG. 3.

When the span structure is assembled as described, the main body portions 16 of the beam members 12 in the lower layer 11a of beam members are spaced apart from but are securely connected to the main body portions 16 of the beam members 12 in the upper layer 1112 by means of the side rail portions 17 and flange portions 18 of the beam members of the lower layer 11a. As a consequence, the main body portions 16 of the beam members 12 in the lower layer 11a and the main body portions 16 of the beam members 12 in the upper layer 1112 of beam members form, in conjunction with the connecting side rail portions 17, a stressed-skin structure that has inherently far greater strength than does the aggregate strength of the individual beam members which comprise the span structure.

The already high strength of the stressed-skin span structure can be greatly increased by introducing a rigid lightweight core material 2 1 having inherently high compressive strength and, advantageously, a relatively high beam strength (i.e., resistance to bending) into the longitudinal box-like voids formed by the channel-shaped beam members 12 of the lower layer 11a and the under surface of the main body portions 16 of the beam members of the upper layer 11b. Lightweight core materials suitable for this purpose include foamed plastics such as foamed polyurethane, foamed poly-vinyl chloride, foamed polystyrene, foamed epoxy resins, foamed phenolic resins, and the like. In addition, foamed concrete can advantageously be employed as the core material when the span structure is being used for, or as a structural element in, a bridge or other heavy-duty, load-bearing structure.

The light-weight core material 21 substantially completely fills the box-like, longitudinal voids between the stressed skins of the span structure and thereby greatly increase the rigidity and load-bearing capacity of the spanstructure. To obtain the maximum benefit from the lightweight core material, in this regard, the lightweight core material is advantageously adhesively secured to the inner surface of the beam members forming the box-like voi-d. Many foamed plastic materials such as the foamed polyurethane and epoxy resins will inherently adhere to the inside surfaces of the beam members. Alternatively, the inner surfaces of the beam members can be coated with an adhesive substance which, when the lightweight core material is introduced into the box-like void, will insure adherence of the foam to the beam members and thereby form a virtually unitary structure. The lightweight core material 21 is preferably introduced in its uncured fluid form into the box-like voids of the span structure after the channel-shaped beam members have been assembled to form the span structure of my invention, the core material then being cured or hardened in situ in the voids.

The load bearing capability of the span structure can be increased almost indefinitely by increasing the number of layers 11 of channel-shaped beam members '12 comprising the span structure. Thus, as shown in FIG. 4, the span structure may comprise four (or more) layers 11a, 11b, 11c and 11d of beam members arranged as previously described. The main body portions 16 of the beam members 12 in each layer cooperate with the main body portion 16 of the beam members 12 in immediately adjacent layers of the assembly to form a multi-layer, stressed-skin structure the load-bearing capacity of which greatly exceeds the aggregate load-bearing capacity of the individual beam members comprising the span structure. Moreover, as also shown in FIG. 4, the uppermost layer 11d of beam members 12 can be covered by and secured to a layer of sheet material 23 which, in cooperation of the main body portion 16 of the beam members 12 in the upper layer 11d, comprises an additional stressed-skin component of the overall span structure. To be effective as a component of the stressedskin span structure the layer 23 should, of course, have approximately the same tensile strength as the main body portion 16 of the beam members 12, and to this end is preferably formed of the same material (e.g., sheet steel) as the beam members. As before, the box-like longitudinal voids present in the span structure are advantageously filled with a lightweight foamed plastic or similar core material 21 which substantially increases the strength and rigidity of the span structure.

As previously pointed out, the channel-shaped beam members 12 may take a variety of forms, some of which are shown in FIG. 5. The channel-shaped beam members 12 shown in FIGS. 5(a) and 5(b) are essentially the same as the channel-shaped beam members shown in FIG. 2. The adjoining beam members 12 shown in FIG. 5(a) are secured to each other by means of a strip or layer of adhesive material such as fabric-reinforced epoxy tape 25. The adjoining beam members 12 shown in FIG. 5(b) are secured to each other by means of channelshaped locking strips or clips 27 which engage the inturned flange portions 18 of adjoining beam members as clearly shown in the drawing. The locking strips or clips 27 may extend the full length of the longitudinal beam members, or they may be disposed at spaced intervals along the length of the beam members. The flange portions 18 of the beam members 12 shown in FIG. 5(a) are formed with mutually cooperating conventional sheet metal lock joints 29 of which a wide variety are known in the art. The side rail portions 17 of the beam members 12 shown in FIG. Std) are themselves channelshaped so that side rail portions 17 of adjoining beam members form a box-like structure 31 which significantly enhances the ultimate strength and load-bearing capacity of the span structure. Other means for joining the beam members together, and other shapes and configurations for the beam members and for the constituent structural elements thereof, will be readily apparent to those skilled in the art.

From the foregoing description of the stressed-skin span structure of my invention, it will be seen that I have made an important contribution to the art to which my invention relates.

I claim:

1. A self-supporting stressed-skin span structure comprising:

at least two layers of longitudinally extending channelshaped beam members each beam member comprising a longitudinally extending main body portion and upstanding side rail portions disposed along the longitudinal edges of said main body portion generally perpendicular thereto, said channel-shaped beam members in each layer being disposed side by side in contact with each other with the open channel of each beam member facing upwardly and with the main body portions of adjoining beam members in substantial horizontal alignment,

the channel-shaped beam members in adjacent layers being disposed with the upper longitudinal edges of the upstanding side rail portions of the beam members in the underlying layer secured to the underside of the main body portions of the channel-shaped beam members disposed immediately thereover,

whereby the longitudinally extending main body portions of the beam members in one layer and the longitudinally extending main body portions of the beam members in adjoining layers of said beam members form a stressed-skin structure that is capable of supporting loads substantially in excess of the aggregate load that can be supported by the individual components of the span structure.

2. The span structure according to claim 1 wherein the box-like longitudinal voids formed by each channel-shaped beam member and the main body portions of the beam members disposed directly thereover are substantially completely filled with a rigid lightweight core material having high compressive strength.

3. The span structure according to claim 2 wherein the lightweight core material is a foamed rigid plastic material selected from the group consisting of foamed polyurethane, polyvinyl chloride, polysytrene, epoxy and phenolic resins.

4. The span structure according to claim 2 wherein the lightweight core material is foamed concrete.

5. The span structure according to claim 2 wherein the lightweight core material is adhesively secured to the inner surfaces of the box-like longitudinal voids.

6. The span structure according to claim 1 wherein the channel-shaped beam members in each layer and in adjoining layers of said beam members are adhesively secured to each other.

7. The span structure according to claim 1 wherein the channel-shaped beam members are provided with flange portions disposed along the upper longitudinal edge of each side rail portion generally perpendicular thereto.

8. The span structure according to claim 7 wherein the flange portions are turned inwardly and wherein adjoining beam members are connected together by small channel-shaped clip members which engage said inwardly turned flange portions.

9. The span structure according to claim 7 wherein the flange portions of adjoining channel-shaped beam members are formed with mutually cooperating lock joints.

10. The span structure according to claim 1 wherein the upper longitudinal edges of the side rail portions of the channel-shaped beam members in the uppermost layer of said beam members are secured to the under surface of a layer of sheet material having substantially the same tensile strength as the sheet material .from which the beam members are made, whereby said layer of sheet material forms an additional stressed-skin component of the span structure.

References ited UNITED STATES PATENTS 2,150,217 3/1939 Gettelman 52-90 X 3,148,230 9/1964 Behner 52-561 X 3,315,424 4/1967 Smith 52-809 X JOHN E. MURTAG'H, Primary Examiner. 

1. A SELF-SUPPORTING STRESSED-SKIN SPAN STRUCTURE COMPRISING: AT LEAST TWO LAYERS OF LONGITUDINALLY EXTENDING CHANNELSHAPED BEAM MEMBERS EACH BEAM MEMBER COMPRISING A LONGITUDINALLY EXTENDING MAIN BODY PORTION AND UPSTANDING SIDE RAIL PORTIONS DISPOSED ALONG THE LONGITUDINAL EDGES OF SAID MAIN BODY PORTION GENERALLY PERPENDICULAR THERETO, SAID CHANNEL-SHAPED BEAM MEMBERS IN EACH LAYER BEING DISPOSED SIDE BY SIDE IN CONTACT WITH EACH OTHER WITH THE OPEN CHANNEL OF EACH BEAM MEMBER FACING UPWARDLY AND WITH THE MAIN BODY PORTIONS OF ADJOINING BEAM MEMBERS IN SUBSTANTIAL HORIZONTAL ALIGNMENT, THE CHANNEL-SHAPED BEAM MEMBERS IN ADJACENT LAYERS BEING DISPOSED WITH THE UPPER LONGITUDINAL EDGES OF THE UPSTANDING SIDE RAIL PORTIONS OF THE BEAM MEMBERS IN THE UNDERLYING LAYER SECURED TO THE UNDERSIDE OF THE MAIN BODY PORTIONS OF THE CHANNEL-SHAPED BEAM MEMBERS DISPOSED IMMEDIATELY THEREOVER, WHEREBY THE LONGITUDINALLY EXTENDING MAIN BODY PORTIONS OF THE BEAM MEMBERS IN ONE LAYER AND THE LONGITUDINALLY EXTENDING MAIN BODY PORTIONS OF THE BEAM MEMBERS IN ADJOINING LAYERS OF SAID BEAM MEMBERS FORM A STRESSED-SKIN STRUCTURE THAT IS CAPABLE OF SUPPORTING LOADS SUBSTANTIALLY IN EXCESS OF THE AGGREGATE LOAD THAT CAN BE SUPPORTED BY THE INDIVIDUAL COMPONENTS OF THE SPAN STRUCTURE. 